Minerai | EPFL Graph Search

NOTOC Un minerai (du latin minera, mine) est une roche contenant des minéraux utiles en proportion suffisamment intéressante pour justifier l'exploitation d'une mine, et nécessitant une transformation pour être utilisé par l'industrie. Par extension, le terme « minerai » peut également désigner directement les minéraux exploités. Types de minerais La plupart des minerais métallifères sont :

des oxydes (bauxite) ;
des sulfures (galène, sphalérite) ;
des carbonates (malachite, sidérite) ;
des silicates (garniérite).

Risque d'épuisement des ressources La civilisation industrielle utilise des quantités importantes de minéraux et de métaux lourds. À la suite d'une demande croissante en métaux et autres ressources minérales, les minerais sont exploités à des teneurs de plus en plus faibles et dans des conditions d'extraction de plus en plus coûteuses (par exemple les puits profonds d'extraction du charbon, ou les sables bitumineux pour le pétrole)

Cell-based Automatic Deformation Computation by Analyzing Terrestrial LIDAR Point Clouds

Pierre-Yves Gilliéron, Bertrand Merminod, Jing Wu

This paper presents a cell-based approach for computing the deformation of a monitored object by analyzing point cloud data from terrestrial lidar. This approach can automatically generate an informative deformation description (called "deformation map") with distinctive deformation characteristics for different partial areas. The approach consists of three major computing steps: (a) "split" - the space of the monitored object is divided into 3D uniform cells, (b) "detect" - deformation parameters for each cell (called "meta-deformation") are estimated by comparing the point clouds in the cell sampled at Epochs I and II, and (c) "merge" - the adjacent cells with similar meta-deformation are combined together in a partial area with a consistent "sub-deformation." The main contributions of this paper ore: (a) a hybrid deformation model for incremental and comprehensive deformation representation, including meta-deformation, sub-deformation and deformation map, (b) a systematic procedure of "split-detect-merge" to automatically and gradually estimate the hybrid deformation model, and (c) a complete validation with a couple of synthetic and real datasets.

2012

Uranium redox transition pathways in acetate-amended sediments

Daniel Scott Alessi, Rizlan Bernier-Latmani, Malgorzata Alicja Stylo, Elena Suvorova Buffat

Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobility of uranium in the environment and the accumulation of uranium in ore bodies, and inform our understanding of Earth's geochemical history. The molecular-scale mechanistic pathways of these transitions determine the U(IV) products formed, thus influencing uranium isotope fractionation, reoxidation, and transport in sediments. Studies that improve our understanding of these pathways have the potential to substantially advance process understanding across a number of earth sciences disciplines. Detailed mechanistic information regarding uranium redox transitions in field sediments is largely nonexistent, owing to the difficulty of directly observing molecular-scale processes in the subsurface and the compositional/physical complexity of subsurface systems. Here, we present results from an in situ study of uranium redox transitions occurring in aquifer sediments under sulfate-reducing conditions. Based on molecular-scale spectroscopic, pore-scale geochemical, and macroscale aqueous evidence, we propose a biotic-abiotic transition pathway in which biomass-hosted mackinawite (FeS) is an electron source to reduce U(VI) to U(IV), which subsequently reacts with biomass to produce monomeric U(IV) species. A species resembling nanoscale uraninite is also present, implying the operation of at least two redox transition pathways. The presence of multiple pathways in low-temperature sediments unifies apparently contrasting prior observations and helps to explain sustained uranium reduction under disparate biogeochemical conditions. These findings have direct implications for our understanding of uranium bioremediation, ore formation, and global geochemical processes.

National Academy of Sciences2013

Distribution of platinum-group elements and Os isotopes in chromite ores from Mayari-Baracoa Ophiolitic Belt (eastern Cuba)

Reto Frei, Anders Meibom

The Mayari-Baracoa ophiolitic belt in eastern Cuba hosts abundant chromite deposits of historical economic importance. Among these deposits, the chemistry of chromite ore is very variable, ranging from high Al (Cr#=0.43-0.55) to high Cr (Cr#=0.60-0.83) compositions. Platinum-group element (PGE) contents are also variable (from 33 ppb to 1.88 ppm) and correlate positively with the Cr# of the ore. Bulk PGE abundances correlate negatively with the Pd/Ir ratio showing that chromite concentrates mainly Os, Ir and Ru which gives rise to the characteristic negatively sloped, chrondrite-normalized PGE patterns in many chromitites. This is consistent with the mineralogy of PGEs, which is dominated by members of the laurite-erlichmanite solid solution series (RuS2-OsS2), with minor amounts of irarsite (IrAsS), Os-Ir alloys, Ru-Os-Ir-Fe-Ni alloys, Ni-Rh-As, and sulfides of Ir, Os, Rh, Cu, Ni, and/or Pd. Measured Os-187/Os-188 ratios (from 0.1304 to 0.1230) are among the lower values reported for podiform chromitites. The Os-187/Os-188 ratios decrease with increasing whole-rock PGE contents and Cr# of chromite. Furthermore, gamma Os values of all but one of the chromitite samples are negative indicating a subchondiritc mantle source. gamma Os decrease with increasing bulk Os content and decreasing Re-187/Os-188 ratios. These mineralogical and geochemical features are interpreted in terms of chromite crystallization from melts varying in composition from back-arc basalts (Al-rich chromite) to boninites (Cr-rich chromite) in a suprasubduction zone setting. Chromite crystallization occurs as a consequence of magma mixing and assimilation of preexisting gabbro sills at the mantle-crust transition zone. Cr#, PGE abundances, and bulk Os isotopic composition of chromitites are determined by the combined effects of mantle source heterogeneity, the degree of partial melting, the extent of melt-rock interactions, and the local sulfur fugacity. Small-scale (mu m to cm) chemical and isotopic heterogeneities in the platinum-group minerals are controlled by the mechanism(s) of chromite crystallization in a heterogeneous environment created by the turbulent regime generated by successive inputs of different batches of melt.

2005

Distribution of platinum-group elements and Os isotopes in chromite ores from Mayari-Baracoa Ophiolitic Belt (eastern Cuba)

Reto Frei, Anders Meibom

2005